Project: 4oz 1A USB Charger

[Wizard of Oz]

So I'm planning a Grand Canyon Corridor R2R2R for early November, and in an effort to save weight, my Iphone 4S is my GPS, music player, camera, camcorder, etc. It's a 6 day trip, so even in airplane mode the whole time, I'm pretty sure it won't make it all the way through. I plan on enjoying music in the evenings and morning, and doing lots of videos and photos. A few years ago I made a 3.2oz USB charger that worked with my old HTC droid and iPod, but it doesn't generate enough juice for my iPhone.

My new design will use a waterproof flexible panel by Powerfilm.

I'm modify the F15-300($60)to eliminate the heaviest parts which is the connector that is hanging on it and the velcro closure. I believe that the panels themselves on the nylon fold-up backing will be 3 oz. and that gives me 1 oz to work with to interface to my USB.

Since I used 6V panels before, I used a linear regulator design on my previous solar panel. But this one will be a 12V panel design, a linear regulator would be very inefficient and I want to harness as much of the 5W power generator as possible. I'm going to use a buck regulator switching design based around a National LM2675-5.0 Eval Board to the heavy lifting.

This should be about 90% efficient which is about as good as I can get and it has great regulation so I don't hurt my iPhone. There's an updated design called the LM22675 with wider input specs, but I couldn't get an eval design and I'm short on time. So I'll be adding the circuitry required to charge the iPhone in both the 500mA (car charger mode) and the 1A (wall charger mode) to hopefully be able to adapt to overcast sun conditions. It should charge it from dead to 90% in 60-120 minutes. I'll also design in an auto shutoff if the sun goes behind a cloud of I leave it out and LED that indicates whether it's outputing the 5V. I found on my old design that if I left a device plugged in when the sun wasn't strong enough, the panel would actually discharge my phone/iPod.

So I know there are other options such as a spare battery or emergency power plug in, but I thought this would be fun and useful. And I'm a geek so I enjoy this stuff. Plus it's fun to try to make the 4oz goal!

I've got alot out of this site, so I thought it would be fun to post progress here, and get input along the way. Your thoughts and ideas would be much appreciated! I'll keep you posted…literally.

[Eric Lundquist]

Is this a Rim to Rim to Rim or Rim to River to Rim trip?

If you're staying at Phantom Ranch you could buy batteries there and use them in a AA iPhone charger.

GPS is unlikely to be needed as the corridor trails are very well marked.

[Wizard of Oz]

It's a Rim to Rim to Rim in November…BRRRR….

We'll be eating at Phantom Ranch on both ways through but alas I couldn't get a night in the dorms there. Plus I'm planning on spending my money on beer and snickers instead of batteries there :)

LOL, GPS isn't for finding my way on the corridor. I like to mark my picture spots with GPS sometimes, so I know exactly where they were taken.

I looked at some AA Iphone charger, and that's def a great option. I love the flexibility of using this for 12V devices as well though. Do you know of a particular good brand/model of AA Phone Charger? Thanks!

[Jack Elliott]

Dear Wiz,

Keep the technical details coming, and I'm waiting to see how the final design works out.

[Bob Gross]

It might be helpful to you to get a schematic on a full blown solar charge controller. That is what is used on a big solar panel, and it takes care of all sorts of things like blocking the reverse current during a cloud. If you could scale that down to small charging like you need, it might be helpful.

All I have are the big solar charge controllers, so I can't help much. They really make life easier in a big rig.

In a lot of rigs, there is a rechargeable battery between the solar panel and the load. That adds weight, but it also regulates the charge properties. It might be worth looking into.

–B.G.–

[Jerry Adams]

What if you connected panel directly to iphone? Would it blow it up?

If you did linear regulator you'de be 83% efficient, which is pretty close to your 90%. Maybe a 1 ohm resistor would be good enough. What if you put in less than 5 volts?

Spare batteries would probably weigh less, but less fun : )

[Franco Darioli]

When I was fiddling with the power Pot and the Bio Lite stove I came across this battery :

2000mAh , output 1000mA/2100mA for $26 .
Oddly the manufacturer of that battery ,totally unrelated to my search, sent me a price list of that and several others.
I can tell you that the 1000 price is not all that much better than the one from this eBay seller

http://www.ebay.com.au/itm/12000mAh-Dual-USB-output-Charger-External-Battery-Power-Bank-Pack-/180951601619?pt=AU_MobilePhoneAccessories&hash=item2a218e51d3
No experience with the seller nor the battery or the manufacturer but it may be worth having a look.
I think that it is about 350g, 12oz.
If the link does not work is listed under
12000mAh Dual USB output charger external battery power bank pack
To add.
I did order that.
I have only tested that by charging my AA and running LED lights, it works for that.
225g for the battery , about 150g with USB cable and adaptors.

[Jack Elliott]

Wizard writes, "Plus I'm planning on spending my money on beer and snickers instead of batteries there."

I see you think like me. Very good!

Franco — that 12 A/h 12 oz battery pack looks like a beast, and at a very reasonable price. Someone, other than me, will need to try it to make sure it's properly-regulated and won't $moke an iPhone.

[David Thomas]

WOZ*: I've long wondered about the approach Jerry mentioned: Directly connect the solar cells to the iPhone. If they max below one amp, won't they be fine (until the iPhone battery is full)? If so, then you just need to disconnect them before the iPhone is fully recharged. Since the iPhone pretty accurately reports its state of charge, you can disconnect at 85-90% and skip all the weight and complications of the circuitry.

An early generation iPhone could serve as a test bed for anything you cobble together.

If you want music, bring a Nano. An iPhone is going to use a lot more power to play music than a Nano (that does nothing but music). Yes, base weight is up, slightly, but there's much less time spent babysitting the batteries in the iPhone.

*I once sold him an Apple II, of all things.

[Jack Elliott]

David, can the iPhone survive 12 or more volts — which is what a solar panel can put out — on its 5V input line?

[Nick Gatel]

Most small 12 volt solar panels actually put out 13v-15v. They have to to overcome the resistance of battery being charged. A regulated 5v charger is probably able to put out close to 7v. Too many volts (and amps) will cook a battery. I have a 250w 12 volt system on my tent trailer and open circuit voltage is over 17 volts.

I played around with a Goal Zero Nomad 7 this summer while camping in our trailer. In perfect sun during optimum sunlight and orientation it took 2.5 hours to bring an iPhone 4 from 0% to 100% at 6,000 feet in the Southern Sirras. If I were inclined to bring electronics backpacking I would opt for spare batteries, which doesn't work for an iPhone and the batterie packs to recharge the phone are too heavy for what they do.

We camp for weeks on end self contained in our trailer without any energy conservation tactics. I am a solar fan. But for backpacking I wouldn't consider it. Of course I never really have a need for battery operated devices, except for an occasional trip where I carry a camera.

[Wizard of Oz]

Franco, That looks really awesome! I'll look into that for sure. Thanks! But definitely not as much fun.

David, no you can't connect a solar panel or 12V directly to the iphone. It will not charge it and will likely ruin it.

So I wanted to try to test my weight goal tonight, so here's what happened…

First I tested to make sure each panel to makes sure they worked, because I'm PRETTY SURE what I did later voids the warranty…

I weighed the 'manufacturers suggested setup' using a mini Cigarette to USB converter which has a 500mA output. (The final version will be a 1A output)

I took the plug apart and found a circuit board inside. The small board included a diode on the +V line to eliminate discharge of the device when there's not enough sun and a automatically resetting fuse rated at about 1.33A at room temperature (no clue what the is actually for).

After I removed the heavy plug, , circuit board, excess fabric, metal eyes, and velcro, I reweighed the panel.

So with a modded panel, stripped down voltage regulator, and mini iPhone cord, I'm at 3.8oz. So it'll take me a while to get the parts and make the final circuit board and waterproof everything, but it seems possible!!! And it's a serious upgrade from my previous .6W version! Over 8 times the power and only .6 oz heavier, that's a good day in the sun! If it works :)

[Wizard of Oz]

I'll look into more commercial solar charger circuitry designs to see if I can glean any more ideas, that a great thought!

Yea, this panel will also output about 17V when unloaded, which is very common for 12V solar panels. Solar Panels need regulation to do just about anything.

A linear regulator basically dissipates the 'excess' voltage into heat, which is why you usually see those little three prong black ICs with metal tabs on the back. That is what I used for my old panel with 6V panels. It's basically a Zener Diode. So the 1V overage at 100MA was dissipating 100mW into heat. I could deal with that. Although that means that it was only .5/.6 efficient or 83%. However using an appropriate linear regulator on a 12V 5W system would dissipate the 7 V overage or 2.9W, which gives me a 2.1/5 efficiency or 42%. pretty crappy, plus Linear regulators don't up the current on the lower voltage, so I'd only get the 400mA to my 5V device, or 2.1W. Using a Boost Regulator is MUCH more efficient, and hopefully will give me 4.5W to my USB port,or .9A. The Boost Regulator basically stores the charge in an inductor and is able to send it back out in little packets as it switches, so there's much less loss and less heat buildup.

Please keep the ideas and thoughts coming! I'm hoping to get the parts in this weekend and be able to do some tests and weights!

[Wizard of Oz]

One more note while I'm thinking of it. The voltage out of a solar panel (before the regulator) will decrease as more current is pulled (lower resistance load).
So this example is a 7.2V 100mA spec'd panel. So as you over draw current (i.e. larger load or lower resistance), the voltage will go down a bit.

So there are two nice thing about the design I'm hoping to use and the iPhone charging feature. First, the Switching (Boost) Regulator only needs 8V to run, so I might be able to squeak a bit more current out of the Solar Panels than they are spec'd to since I can pull them right down to 8V and still have a solid output for the USB port. BUT that assumes solid full sunlight! That's why I'm going to try to include a switch so I can change the iPhone charging mode from 'wall' to 'car'. Basically, if I don't have enough sun to keep the 5V going in 'wall' mode (the phone pulls 1A or has a 5ohm charging resistance) which may cause too far of a drop of the panel output voltage in lower light conditions, I'll disconnect it, switch my solar charger to 'car' mode, and reconnect it which will change the PHONE to 10ohm charge resistance or .5A draw allowing my solar panel voltage output to rise hopefully high enough to continue to charge even in poor conditions.

As I mentioned before, I also plan to include a small 3mA LED to let me know when the 5V is being output properly (iPhone is charging), and I will include a circuit that will turn off the regulator output if the panel voltage drops below 8V. I think this combination of features will make it really usable in the field and allay some of the normal concerns and hassles with solar chargers. But, as has been mentioned, I will still have to babysit a bit,hopefully for only an hour or so a day if I'm blessed with clear skies, and hopefully while taking in SPECTACULAR inner canyon views, and a crazy expensive Phantom Ranch Beer! So I won't complain too much for the privilege of tunes, pics and videos to my hearts content! If it works…

[Bob Gross]

A couple of comments. One is the 3mA LED. That is small, but it will be burning all of the time even when you know that charging is happening. Instead, drop some teeny tiny switch in series with it. That way, you can push the switch button and see what you have, but then you release it and there is no 3mA drain.

If you are getting about 17V open circuit in a big solar panel, that is pretty good. As a general rule, only the fairly good solar panels will get you 17V, and many of the cheaper and lighter panels get you only 15 or 16V open circuit. I guess this thing you are doing now is aimed more for 7.2V.

Everything that I have done is with a big panel, so I think only in terms of nominal 12V, so I don't want to steer you wrong about this smaller scale rig.

I was trekking in Nepal, and I was eating dinner in a Sherpa lodge that was candlelit. The proprietor went into the back room and then carried out a 12V car battery. He sat it down on the table and set up a battery operated slide projector. After showing slides of himself on Mount Everest in 1972, he explained the problem to me. He had a good solar panel on the roof, but his charge controller had failed, so he was trying to do things the hard way. I studied it and agreed that it was a charge controller problem. So, when I got home, I ordered up a perfect-size charge controller, received that, and then sent it to San Francisco to his employer. They sent it over to Nepal in a satchel, he hooked it up by my diagram, and it worked. So, now they show more slide shows, solar powered.

–B.G.–

[Jack Elliott]

Thanks for the update, Wizard. Sounds like you're on the right path here.

Next step: make a version to sell.

[Jerry Adams]

I just connect 12 V solar panel directly to car battery – a controller just adds inefficiency.

Like in Wizard's chart, the voltage drops by itself to reasonable voltage for battery.

You have to disconnect it at night.

This may or may not be applicable to Wizard's problem – but I wouldn't try it on my ipod – if I had one

It would be better if it was a 6 Volt panel

[Jack Elliott]

Bob, I think the added complexity and possible decreased reliability by adding a switch isn't worth it. 3mA compared even with "car" (0.5A) mode is only stealing, like, 0.6% of the regulator's output.

[Jack Elliott]

BTW, the iPhone is a USB-powered device, and the spec for USB power is 5.00 ±0.25 V

So it's likely not designed to be connected to a 6 or greater voltage source. Unlike a big ol' lead acid battery, which can soak up a lot of current, overvoltaging the iPhone's DC input circuitry is likely to end up badly.

[Bob Gross]

"Every little bit helps" said the woman who p!ssed into the sea.

–B.G.–

[Bob Gross]

"a controller just adds inefficiency."
"You have to disconnect it at night."

How do you monitor for overvoltage disconnect and undervoltage disconnect? How do you do equalization? You don't need some of these features if you have no battery in the middle.

Charge controllers are very handy.

My point was to study which of the features might be handy for little or no penalty, and roll them in.

–B.G.–

[Stuart R]

WOZ: That graph is the key to understanding pv solar panels. Note that as the load attempts to draw more current, the voltage goes down. 7.2V is the point of maximum efficiency for conversion of light to electricity. So, if you hook a 7.2V panel directly to a 6V battery, the panel will simply supply as much current as it can at 6V, (the voltage on a charging battery does not change much). You need a reverse blocking diode, but otherwise this is a very electrically efficient system. A linear regulator can also be used to prevent overcharging/overvoltage but adds nothing to the overall efficiency.

Now, an active regulator is a different beast – it will draw as much power as it needs to supply its load. So, if you want to supply a load of say 5V @ 1A, the regulator will draw 5/0.9 = ~5.5W from the panel. IF you have sufficient area of panel with sufficient sunlight intensity to supply this power, then ok. But in less optimal conditions, as you attempt to draw more current from the panel, the voltage goes down = LESS power. The regulator will drop out, but then the panel voltage will come back and you get in a cycle of oscillations. A (normal) active regulator will not work unless you have oversized panels that can always supply sufficient power.

[Bob Gross]

"That graph is the key to understanding pv solar panels."

As Stuart points out, the graph is the key.

Most single crystal silicon panels have similar curves, although some are slightly shifted. So, you really need to work with the curve for your specific panel product, and you don't want to just blindly assume a curve that somebody else has for a different one.

Personally, I am a big believer in reverse blocking diodes, typically with very low voltage across it.

Linear regulators were good about twenty years ago, but active regulators are in now.

Once you get the charger thing cooking just right, you can play around with setting it to the sun angle above the horizon, tracking the sun from east to west, and all sorts of things to improve total charging performance. A dinky shadow can really foul it up.

–B.G.–

[Wizard of Oz]

Bob, that's a really good idea that never crossed my mind. I was thinking a single 3mA LED for low drain, but with a 'test' switch, I could put a descent brightness LED on there, or maybe a few SMD indicators to see how much the panel is producing and I no longer have to worry about the loss. That would definitely increase my options without sacrificing any performance (other than a few grams of weight). Plus brighter LEDs could be easier to see in bright light, which by definition is the condition that I'd prefer to use the panel! Thanks! BTW, I am using a 12V spec'd panel, the 7.2V was just an example. It was actually cheaper to buy this Powerfilm 5W unit rather than 5W of 6 or 7 Volt Panels. I'm not sure why that is. All the wiring in the panel unit is inside the stitching so I can't really see how they are wired to guess what spec panels they are and series vs parallel design. BTW, the quality of the build on the Powerfilm is fantastic! High quality wire, Brass rivets (non-corrosive), electrical parts are sealed with silicon and routing and wiring is taped in place to minimize stress. I was very impressed when I took it apart! The little circuit board has two diodes on it and only one is being used, so it must be a generic PCB that they used for their 10W version as well, which is basically 2 of mine in parallel.

Jerry, battery charging is freakishly complex! Luckily the iPhone has alot of built in protection so as long as I stay in the USB 4.75-5.25V spec, I should be ok. You can actually charge batteries at a fairly wide range but it will affect their lifespan and cause excess heat. One of the huge advantages of Lithium Ion batteries, besides their low weight, is the ridiculous # of charge cycles that they can go through. Technically each charge takes a little bit of their capacity away, but poorly designed/spec'd chargers make it much worse. Lead Acid batteries are much more forgiving except that they can heat up and be damaged if overcharged, especially at high (quick) charging voltages. But obviously, the assumption is that if you're charging your car with a solar panel, your battery is dead, and you just want to up the juice, not replace your alternator with a solar panel :)

Jack, think I'm into this one for $100 bucks already :) I'm not sure how well they would sell at that price! But maybe this project will give me some insight into building another one much cheaper. NOW TAKING ORDERS!!! (MUST PAY UP FRONT!!!)

[Jerry Adams]

Two problems with solar panel into lead acid batteries:

You want to keep the battery fully charged. If you don't have enough panel then the battery will be undercharged and over time it can kill the battery, like if the battery goes below 50% charged or so.

If you over-charge the battery, the water in the electrolyte get's conveted to hydrogen and oxygen. If it goes low enough and exposes the plates inside the battery, that will kill the battery.

If you have solar panels on your house charging batteries, you need good controller to prevent these problems. You won't remember to do it manually reliably enough.

If you're vacationing and hooking up the panel each day, you can remember to check and prevent. And disconnect at night to prevent reverse current. The controller and blocking diodes consume some of the power.

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